1. Field of Invention
The present invention belongs to a technical field of an information recording/reproducing apparatus by which information is recorded on a recordable optical disc and is reproduced therefrom. More particularly, the invention relates to a technique for stably detecting pre-pits provided on the optical disc.
2. Description of Related Art
As an information recording medium on which information is additionally writable or rewritable, there is known a disc such as a CD-R (Compact Disc-Recordable), a DVD-R (DVD-Recordable), a DVD-RW (DVD-Rewritable), etc.
In order to record information on its non-recorded area, the above disc is formed with groove tracks (recording tracks) that are slightly wobbled in the radial direction of the disc. The groove track is formed on the disc in correspondence with a wobble signal obtained by frequency-modulating a carrier wave of a prescribed frequency by pre-information indicating the position information and the like of the track on the disc.
In order to extract the wobble signal from the groove track, a reflected light of the radiated light beam reflected from the groove track is received by a photo-detector that is divided into two parts by a dividing line that is optically parallel with a direction tangential to the groove track. Then, a difference signal between the outputs from the respective detectors is generated, and that difference signal is supplied to a BPF (Band Pass Filter), the central frequency of which is the above-mentioned prescribed frequency.
The above-described disc is rotated so that the average frequency of the wobble signal extracted by the BPF is equal to the above-described prescribed frequency. At this time, the wobble signal thus extracted (hereinafter called “the extracted wobble signal” as well) is also used as a reference signal to produce a clock signal for recording (hereinafter referred to as “recording clock signal”). Namely, the extracted wobble signal is a continuous signal having a frequency component synchronized with the rotation of the disc. By producing a clock signal synchronized, in phase, with such continuous signal, the recording signal exactly synchronized with the rotation of the disc is generated.
Also, in addition to the fact that the groove tracks are wobbled, so-called “pre-pits” are formed on each of land tracks adjacent to the groove tracks at prescribed intervals. The pre-pits are also used for adjusting the phase of the recording clock signal that has been produced from the extracted wobble signal. Since the pre-pits are formed, in advance, on the information recording area of the disc at prescribed intervals, the information recording/reproducing apparatus produces the recording clock signal according to the extracted wobble signal and also adjusts the phase of the recording clock signal based on the detected result of the pre-pits. Thus, the information recording/reproducing apparatus produces a correct recording clock signal for recording information onto the disc and performs recording of information according to the correct recording clock signal.
In one or some of the above-described discs, the groove track for recording information is discontinuously (intermittently) formed in the lead-in area where information relating to the copyright and/or information for preventing the unauthorized copy are recorded. Namely, the groove track is continuously formed in the data area for recording information. On the contrary, as a result of the groove track being discontinuously formed, that area has such a configuration that concavities and convexities are repeatedly formed on the surface of the disc (hereinafter such portion is also called “the emboss area”).
In the non-recorded disc such as a DVD-RW or else, there is beforehand recorded important information such as information for preventing the above-described unauthorized copy in the emboss area within the lead-in area, and that information is of course readable. However, within the emboss area, even when recording information with an aim to rewrite that important information illegally, since the recording groove track is formed intermittently, the overwritten information cannot correctly be reproduced. Therefore, it is possible to prevent important information associated with unauthorized copy and so on from being illegally rewritten.
However, there is such a problem that, since the groove track is intermittently formed within the emboss area, the noise components of the extracted wobble signal including the pre-pit signals increase, and it becomes difficult to stably perform the detection of the pre-pit signals. For this reason, in the so-called “finalizing processing” executed at the time of ending recording of information onto the disc, the recording clock signal becomes unstable and the finalizing processing cannot be executed correctly.